Multi-Physics Models for Proppant Placement in Energy Georeservoirs

地下能源技术在当代地质力学中至关重要，包括增强型地热系统(EGS)。EGS使用地热能从地下深处炎热的渗透性增强的岩层中发电。该项目解决了地热能回收过程中对更有效的支撑剂(保持裂缝开放的颗粒状材料)使用的需求。具体地说，支撑剂放置问题的解决将有助于地质油藏的优化、增长和进一步开发，并将加快EGS技术从目前的早期开发阶段向商业使用的转变。这将有利于全球可再生能源市场和全球可持续能源交付。这项研究还有可能有助于定量了解几个额外的地质力学问题，如泥石流和泥浆流、大坝的内部侵蚀和建筑物周围土壤的冲刷。这项研究推进了稠密悬浮体流动的基本物理知识，并发展了新的理论，将改进支撑剂放置到具有不规则、粗糙表面的分支水力裂缝的工程设计中。由这一活动产生的模型将首次通过考虑颗粒-颗粒相互作用和流体流体动力之间的相互作用以及流体、颗粒和裂缝属性的作用来捕捉颗粒团聚。我们的多学科团队由一名岩土工程师和一名数学建模师组成，将与其他项目合作，通过研究、工程和教育活动扩大女性和其他代表性不足群体在科学领域的参与。该项目旨在更好地了解和缓解水力压裂中支撑剂注入过程中导致支撑剂测井的情况。该项目的产品将导致在渗透性增强过程中有效地放置支撑剂，潜在地减少其对环境的影响。这个项目的首要目标是对这一现象进行定量的理解，并需要发展新的数学理论。目前预测支撑剂流动和输送的实践依赖于实验室测试中建立的经验关系，这些经验关系涉及大宽度、光滑、直的狭缝，适合用于简化的单裂缝模型。然而，大多数水力裂缝是粗糙的和分支的，这为流体和支撑剂的运输创造了一条复杂的路径。稠密泥浆流动和输送的物理学包括颗粒-颗粒和流体-颗粒相互作用。特别是对于用于支撑剂放置的流体，这一物理没有得到正确的理解，因此在当前的模型中没有得到充分的解释。建立了真实裂缝网络中支撑剂流动的数学模型，并用实验室规模的实验进行了验证。该实验组件包括使用压裂测试扫描的岩石表面在3-D打印裂缝中进行的下一代缝隙流动实验。骨折处将使用透明材料打印，从而能够使用粒子图像测速仪(PIV)跟踪支撑剂颗粒的运动。该项目的理论部分由两个相互关联的部分组成，一个是考虑颗粒-颗粒和颗粒-流体相互作用的连续介质尺度本构关系的发展，另一个是发展一种计算高效的算法，用于模拟具有粗糙壁面和(随机)变化孔径的裂缝中的支撑剂流动。连续介质模型将被参数化为反映裂缝表面粗糙度、平均裂缝宽度以及流体和支撑剂颗粒的物理和力学特性的参数。这些和其他有效的模型参数将通过离散的数值模拟和缝隙流动实验来确定。该模型将为油藏工程师确保支撑剂在水力裂缝中的正确放置以及预测和规划地质油藏可靠的渗透率增强提供实用工具。

Underground energy technologies are of crucial importance in contemporary geomechanics, including Enhanced Geothermal Systems (EGS). EGS use geothermal energy to produce electricity from hot deep underground permeability-enhanced rock formations. This project addresses the need for more effective proppant (granular material that keeps the fractures open) usage during geothermal energy recovery. Specifically, resolving proppant placement issues will aid optimization, growth and further development of georeservoirs, and will speed up transformation of the EGS technology from its current early development stage to commercial use. This will benefit global renewable energy market and global sustainable energy delivery. This research has also a potential for contributing to quantitative understanding of several additional geomechanical issues, such as mud flows and slurry flows, internal erosion of dams and scouring of soil around structures. This research project advances the knowledge of fundamental physics of flow of dense suspensions, and develops new theories that would improve engineering design for proppant placement into branching hydraulic fractures with irregular, rough surfaces. The models resulting from this activity will, for the first time, capture particle agglomeration by accounting for the interplay between particle-particle interactions and fluid hydrodynamic forces and the role of fluid, particle and fracture properties. Our multidisciplinary team, consisting of a geotechnical engineer and a mathematical modeler, will collaborate with other programs to broaden participation of women and other underrepresented groups in science through research, engineering and educational engagements.This project seeks to better understand and mitigate the conditions resulting in proppant logging during proppant-fluid injection into hydraulic fractures. The project products will lead to efficient proppant placement during permeability enhancement, potentially reducing its environmental impact. The overarching goal of this project is to gain quantitative understanding of this phenomenon and requires development of new mathematical theories. Current practice for predicting proppant flow and transport relies on empirical relationships developed from laboratory tests involving large width, smooth, straight slots, appropriate for use in simplified single-fracture models. However, most hydraulic fractures are rough and branching, which creates a complex path for the fluid and proppant transport. The physics of dense slurry flow and transport includes particle-particle and fluid-particle interactions. Especially for fluids used in proppant placement, this physics is not properly understood and, hence, not adequately accounted for in current models. A mathematical model of proppant flow in realistic fracture networks will be developed, and validated with laboratory-scale experiments. The experimental component comprises next-generation slot-flow experiments in 3-D printed fractures using scanned rock surfaces from fracturing tests. The fractures will be printed with transparent materials, enabling the use of Particle Image Velocimetry (PIV) to track the movement of proppant particles. The project's theoretical part consists of two interrelated components, development of a continuum-scale constitutive law that accounts for particle-particle and particle-fluid interactions, and development of a computationally efficient algorithm for modeling proppant flow in fractures with rough walls and (randomly) varying apertures. The continuum-scale models will be parameterized with parameters reflecting properties of fracture surface's roughness, average fracture width, and physical and mechanical properties of fluid and proppant particles. These and other effective model parameters will be determined from both discrete numerical simulations and slot-flow experiments. The model will serve as a practical tool for reservoir engineers to ensure the proper proppant placement in hydraulic fractures and to predict and plan the reliable permeability enhancement of georeservoirs.